George Mason III drowned on March 5, 1735, when a storm overturned his boat as he crossed the Potomac River between plantations. His death was a river accident, and the available account does not describe a preceding fatal illness. Mason's extensive property and regular movement between lands on either side of the river explain the setting of the journey, but do not establish the boat's precise route or the weather's detailed course. No securely matched eyewitness account of his final actions, rescue attempts, or last words has been established here. His widow, Ann Thomson Mason, and their children subsequently returned to Chopawamsic. Their son George, later the author of the Virginia Declaration of Rights, was still a boy, and the loss left the household and the management of a substantial estate in changed circumstances. At the time of the drowning Mason held extensive acreage in Stafford County. The circumstances supported by the biography are the crossing, the storm, the capsizing, and the drowning. His son's later Revolutionary career and death belong to a different generation.